This project is aimed at defining stimulus-response relationships involved in the physiological control of LH, FSH, prolactin and TSH secretion in the rat. Part of the program deals with applications of secretory kinetic theory to the analysis of pituitary hormone synthesis and release rates. Analytical methods include: radioimmunoassay of stored and circulating pituitary hormones; gross and histological examination of the pituitary and target organs; measurements of target gland hormone concentrations in the serum. Another part of the program deals with definition and characterization of the interactions of releasing-factors (i.e., GnRH) and long-loop feedback hormone(s) (i.e., dihydrotestosterone, estradiol, etc.) at the pituitary level. Current and proposed work is focused primarily on direct feedback effects of androgens on LH secretion in the male rat, in vivo and in vitro. A third aim of the program is development and implementation of methods (direct, it possible) for evaluating feedback (and other effects) on releasing factor secretion. an eventual aim of these studies is to characterize the relative roles played by both direct and indirect feedback, and other regulatory influences, in physiological control, and also in pituitary responses to non-physiological (experimental, pathological) situations. The overall, broadest, scope of these studies is to define various sites within these brain-pituitary-target gland systems at which physiological control mechanisms could be expected to operate and then to define whether and when these mechanisms actually come into play.